If he didn't take me by surprise, then I would try to block his attack, and likely pin him for police pick-up.
Strangers running around attacking people is a threat not just to me, but to others. What if this crazy guy decided that for his next trick he was going to run up to that woman carrying a baby, and punch the baby's head?
No. He must be
removed as the threat to human safety that he is.
By "removed", I mean incapacitated until he sobers up, or otherwise comes back to his senses. If this means spend a night in jail, or in the mental hospital, or pinned to the ground, or lying in a hospital bed with several broken limbs......that would be up to him, and my access to calling the police.
I would try not to permanently maim him or kill him. I would not have anger/hatred toward him. After he was secured by whatever means, then I would probably just walk away, shaking my head about how crazy humans can be.